Aged 96, Queen Elizabeth has died in Balmoral after the longest reign in British history.
She died peacefully, surrounded by family at Balmoral Castle in Scotland.
Her death sets in motion Operation London Bridge, the plan that reportedly lists what will happen in the United Kingdom following the monarch's death.
Listen to Mamamia's daily news podcast The Quicky, which explains more about Operation London Bridge. Post continues.
The code word "London Bridge is down" was used to inform the British prime minister and Privy Council of her passing at 4:30pm (1:30am AEST), with flags on government buildings at half mast 10 minutes after the announcement.
A footman pinned an official notification of the Queen's death on the gates of Buckingham Palace and her Scottish residence, as the UK begins 10 days of mourning.
The Palace sent the news out to the world's media via the press association, and the royal website homepage turned black. TV presenters across the Commonwealth were instructed to wear black, as per strict protocols, with all regular programming suspended.
Here's everything we know about what happens next:
While we don't know exactly when the Queen's funeral will be, it's likely to be after the 10 days of mourning is complete.
The day will be a Day of National Mourning in Britain and a two-minute silence will be observed across the country at midday.
After her coffin returns to London in coming days, the Queen will lie in state in Westminster Hall for three days, allowing members of the public to file past.
The last member of the royal family to lie in state in the hall was the Queen's mother in 2002. Over 200,000 people visited her coffin.
The Queen's funeral will be held at Westminster Abbey, and she will be buried at Windsor Castle next to her late husband Prince Philip and her father King George VI.
Upon the death of his mother, Charles immediately ascended to the throne.
In the past year, Charles has taken on increased responsibilities as the Queen's health ailed; including opening parliament in May and stepping in for her on Remembrance Sunday, the Commonwealth Day Service and the Easter Service.
He must now choose his regnal name - the BBC is reporting he will be known as King Charles III.
He could have chosen any of his four names; Charles, Philip, Arthur, George.
It's not known yet when Charles' coronation will take place, but reports suggest it could be several months away.
As tradition dictates, the first public proclamation of the new monarch will be read in the open air at St James's Palace by the garter king of arms, in the presence of the earl marshal and the sovereign's serjeants-at-arms.
This will likely happen tomorrow, a day after the Queen's passing.
After that, Charles will read a declaration and take an oath to preserve the Church of Scotland and the Church of England.
After the proclamation at St James, similar ceremonies will be held in Edinburgh, Windsor and York.
Although he is heir to the throne, Prince William will not automatically become Prince of Wales - that will have to be conferred on him by his father.
If this is confirmed, Kate will become the Princess of Wales a title previously held by William's mother Diana.
William has, however, already inherited his father's title of Duke of Cornwall, which traditionally goes to the eldest son of the monarch.
William and Kate are now titled Duke and Duchess of Cornwall and Cambridge, a title change that their social media already reflect.
Camilla will also get a new title - she will now become the Queen consort (consort means spouse of the monarch).
God Save the Queen will now be reverted back to the previous anthem of God Save the King - which holds the exact same lyrics, but with the words and pronouns changed to the male version.
It was last used when the Queen's father was on the throne in 1952.
In Australia, flags will fly at half-mast for the next 10 days except when the accession of the new monarch is proclaimed.
A gun salute took place at Parliament House in Canberra at dusk to mark her passing, it consisted of one round for each year of The Queen's life at 10 second intervals.
Over the weekend, a proclamation ceremony will be held at Parliament House in Canberra - the event is open to the public. It will be read by the governor-general and will be followed by a 21-gun salute.
In Australia, there will be no official mourning period as there is in the UK.
Australian representatives (likely the PM and the governor general) will attend her funeral in the UK, with a memorial service expected to take place here on their return.
The Australian reports a new national day of commemoration, likely to be a public holiday, could form part of Australia's response to the news.
Feature image: Getty/Mamamia.